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Journal of Experimental Biology 49,565-582 (1968)
Published by Company of Biologists 1968

On Respiration in the Dragonet Callionymus Lyra L

G. M. HUGHES ¹ and SHUN-ICHI UMEZAWA ²

¹ The Plymouth Laboratory; Department of Zoology, University of Bristol Bristol, BS 81 UG
² The Plymouth Laboratory; Department of Biology, University of Kochi, Japan

1. The usefulness of a bottom-living fish, the dragonet (Callionymus lyra), in experiments on fish respiration is described. The position and nature of its opercular opening made it possible to determine directly the volume of water pumped over the gills and the PO₂ of the mixed expired water. The normal ventilation volume for a 100 g. fish was about 30 c.c./min.

2. The relationship between cardiac and respiratory rhythms was investigated and showed a variety of ratios. The heart usually beats more than once during each respiratory cycle. Individual variations in the coupling between these rhythms was common and close couplings were observed in the absence of anaesthetic and at normal PO₂s.

3. Changes in minute volume produced by altering the hydrostatic pressure across the respiratory system did not affect the heart rate. Percentage utilization fell at higher flow rates. Changes in flow per cm. of water pressure gradient was less with negative gradients than when the static pressure on the mouth side exceeded that in the opercular collecting chamber.

4. Oxygen consumption of the fish is directly related to the ambient PO₂ over a wide range (30-120 mm. Hg). Sudden lowering of the PO₂ in the inspired water leads to compensatory responses in which the minute volume is maintained or increased as a result of a rise in stroke volume and lowered respiratory frequency: there is also a marked bradycardia. During recovery the increased oxygen consumption of the fish resulted from a rise in utilization rather than a change in the respiratory rate or ventilation volume.

5. Analysis of the time course of the changes in heart rate and ventilation volume in experiments in which PO₂ was changed supports the view that the receptors mediating bradycardia occur on the gills and respond directly to the change in PO₂ rather than to the secondary increase in flow produced by the hypoxia.